New unsaturated 1,8-naphthalimide dyes for use in nematic liquid crystals

The properties of new fluorescent dyes (derivatives of unsaturated 1,8-naphthalimide) are studied. Spectral characteristics of the dyes are recorded in both isotropic (ethanol, dioxane) and anisotropic (nematogenic liquid crystal mixture ZLI 1840) media. The optical, electro-optical, and thermodynamical properties of the liquid crystal-dye mixtures are examined. The orientational order parameters are evaluated to be within 0.4-0.5, depending upon the dye's molecular structure. Additionally, the influence of chemical bounding of the dyes to polystyrene chains on the phase transition temperature from the nematic to the isotropic state of polymer/liquid crystal mixtures is investigated. The low-molecular-mass dyes do not markedly affect the clearing point of pure liquid crystal, while the dye-styrene copolymers lower the transition temperature and widen the two-phase region at the transition. The electro-optical properties of the dye/liquid crystal systems imply potential utilization of the dyes studied in the so called ''guest-host'' liquid crystal displays.